Interaction matters: synergy between vermicompost and PGPR agents improves soil quality, crop quality and crop yield in the field

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Abstract

Organic amendments not only promote soil quality and plant performance directly but also facilitate the
establishment of introduced microbial agents. A field experiment with a fully factorial design was
conducted using three levels of vermicompost (without vermicompost, low dose of 15Mgha 1 and high
dose of 30Mgha 1), with and without plant growth-promoting rhizobacteria (PGPR) to investigate their
effects in a tomato – by spinach rotation system. Our results demonstrated that applying PGPR alone had
no effect on soil properties and crop performance. Vermicompost enhanced the beneficial effects of PGPR
on both soil and crop, with the extent of promotion depending on the dose of vermicompost and crop
types. In the presence of vermicompost, PGPR significantly (P<0.05) reduced soil carbon and nitrogen
but increased soil microbial biomass carbon and nitrogen. PGPR also significantly increased the yield of
tomato and spinach under the low dose of vermicompost, but only significantly increased tomato yield
under the high dose of vermicompost. There were strongly synergistic effects between vermicompost
and PGPR on crop quality, with crop nitrate concentration being significantly decreased, while the
vitamin C in tomato and soluble protein in spinach was significantly increased. Our results revealed the
high potential of integrating vermicompost and microbial agents to substitute for regular chemical
fertilization practices.